1. Field of the Invention
The present invention relates to a magnetic head for perpendicular magnetic recording that is used for writing data on a recording medium by means of a perpendicular magnetic recording system, and more specifically, to a magnetic head for perpendicular magnetic recording that has a write shield.
2. Description of Related Art
The recording systems of magnetic recording devices such as magnetic disk drives include a longitudinal magnetic recording system wherein signals are magnetized in a direction along the plane of a recording medium (the longitudinal direction) and a perpendicular magnetic recording system wherein signals are magnetized in a direction perpendicular to the plane of a recording medium. It is known that the perpendicular magnetic recording system is harder to be affected by thermal fluctuation of the recording medium and capable of providing higher linear recording density, compared with the longitudinal magnetic recording system.
Magnetic heads for perpendicular magnetic recording typically have, like those for longitudinal magnetic recording, a structure in which a read head unit having a magnetoresistive element (hereinafter, also referred to as MR element) for reading and a write head unit having an induction-type electromagnetic transducer for writing are stacked. The write head unit includes a main pole that produces a write magnetic field in a direction perpendicular to the plane of a recording medium.
In a magnetic disk drive, the magnetic head is mounted on a slider that flies slightly above the surface of a recording medium. The magnetic head has a medium facing surface to face the surface of the recording medium. The recording medium includes a magnetic recording layer. Tracks are concentrically formed in the magnetic recording layer. The tracks are the area of the magnetic recording layer on which data is to be written.
Here, the side of the positions closer to a leading end relative to a reference position will be defined as the leading side, and the side of the positions closer to a trailing end relative to the reference position will be defined as the trailing side. The leading side is the rear side in the direction of travel of the recording medium relative to the slider. The trailing side is the front side in the direction of travel of the recording medium relative to the slider.
The magnetic head is typically disposed near the trailing end of the medium facing surface of the slider. In a magnetic disk drive, positioning of the magnetic head is performed by a rotary actuator, for example. In this case, the magnetic head moves over the recording medium along a circular orbit about the center of rotation of the rotary actuator. In such a magnetic disk drive, a tilt of the magnetic head with respect to the tangent of the circular track, which is called a skew, occurs according to the position of the magnetic head across the tracks.
In particular, in a magnetic disk drive of the perpendicular magnetic recording system which is higher in capability of writing on a recording medium than the longitudinal magnetic recording system, the skew mentioned above can cause the phenomenon that signals already written on one or more tracks in the neighborhood of a track targeted for writing are erased or attenuated during writing of a signal on the track targeted for writing. In the present application, this phenomenon will be called unwanted erasure. Unwanted erasure includes adjacent track erasure (ATE) and wide-area track erasure (WATE). To achieve higher recording density, it is necessary to prevent unwanted erasure.
In order to prevent unwanted erasure induced by the skew and achieve higher recording density, it is effective to provide a write shield in the vicinity of the main pole. For example, U.S. Patent Application Publication No. 2005/0128637 A1 discloses a magnetic head having a write shield (a first side shorting shield, a second side shorting shield, a top shorting shield, and a bottom shorting shield) that has an end face wrapping around an end face of the main pole in the medium facing surface.
U.S. Pat. No. 7,365,943 B2 discloses a magnetic head having a write shield (a shield yoke) that has end faces located in the medium facing surface at positions on opposite sides of the end face of the main pole in the track width direction.
The write shield has the function of capturing a magnetic flux that is produced from the end face of the main pole and spreads in directions other than the direction perpendicular to the plane of the recording medium, so as to prevent the magnetic flux from reaching the recording medium. A magnetic head having the write shield is capable of preventing unwanted erasure and capable of providing further improved recording density.
To make full use of the function of the write shield, it is preferred to provide a return path section for connecting the write shield and a part of the main pole located away from the medium facing surface to each other. The write shield and the return path section allow a magnetic flux that has been produced from the end face of the main pole and has magnetized the recording medium to flow back to the main pole. In the magnetic head disclosed in U.S. Patent Application Publication No. 2005/0128637 A1, a first return pole located on the trailing side relative to the main pole and a second return pole located on the leading side relative to the main pole constitute the aforementioned return path section.
The magnetic head disclosed in U.S. Pat. No. 7,365,943 B2 is provided with a return yoke connected to a part of the main pole located away from the medium facing surface. However, the write shield (the shield yoke) is not connected to the return yoke. In this magnetic head, the write shield is prone to flux saturation and thus it is difficult to make full use of the function of the write shield.
In a magnetic head having the write shield and the return path section, there is a space defined by the main pole, the write shield and the return path section. A coil is provided to pass through the space. The coil is driven by a write signal.
To prevent unwanted erasure, it is particularly important to capture a sufficient amount of magnetic flux into the write shield from two portions of the end face of the write shield that are located on opposite sides of the end face of the main pole in the track width direction, and to keep the magnetic flux having been captured into the write shield from leaking out of the write shield.
In the magnetic head disclosed in U.S. Patent Application Publication No. 2005/0128637 A1, a magnetic flux having been captured into the write shield from each of the two portions of the end face of the write shield that are located on opposite sides of the end face of the main pole in the track width direction bifurcates into two separate flows: one toward the first return pole located on the trailing side relative to the main pole; and the other toward the second return pole located on the leading side relative to the main pole. At this time, the magnetic flux passes through a magnetic path composed of a plurality of magnetic layers stacked one on another. The magnetic path includes one or more boundaries between two adjacent magnetic layers, the one or more boundaries being exposed in the medium facing surface. In the vicinity of the one or more boundaries, magnetic flux tends to leak from within the magnetic path to the outside thereof. This may result in the occurrence of unwanted erasure.
With increases in frequency of write signals for higher recording densities, it is required of the write head unit to provide an improved rate of change in the direction of the magnetic flux produced from the end face of the main pole. To satisfy this requirement in the magnetic head having the write shield and the return path section, it is effective to reduce the return path section in length. To that end, it is effective to reduce the number of turns of the coil. Reducing the number of turns of the coil, however, results in a smaller magnetomotive force of the coil and thus gives rise to the problem that the minimum value of the write current required to obtain desired write characteristics, which will hereinafter be referred to as the minimum write current value, is increased.